Seven civilians have been shot dead by Kenyan troops advancing towards the al-Shabab stronghold of Kismayo, a Somali army spokesman has told the BBC.
"It was a deliberate killing," said Adan Mohamed Hirsi.
The Kenyans are part of the pro-government African Union mission in Somalia, which says it is investigating the incident.
The alleged shooting happened about 50km (30 miles) from Kismayo, the largest city still in militant hands.
Kenyan troops intervened in Somalia a year ago after a spate of cross-border attacks blamed on the al-Qaeda linked al-Shabab group.
Mr Hirsi condemned the latest killings and asked the Somali government to take action.
"This incident is very hurtful," he told the BBC's Somali service, adding that two civilians were seriously wounded.
Col Ali Aden, a spokesman for the African Union mission, known as Amisom, confirmed to the BBC that Kenyan and Somali troops were operating together in the village of Janay Abdalla.
He said that appropriate action would be taken after the investigation was completed.
Al-Shabab has been forced out of the capital, Mogadishu, and several other towns over the past year but still controls much of the countryside in south and central Somalia.
However, it still stages frequent attacks.
On Saturday, gunmen shot dead a member of Somalia's new parliament in Mogadishu.
Mustafa Haji Maalim was gunned down after leaving a mosque in the southern Waberi district following evening prayers, witnesses said.
The dead lawmaker was the father-in-law of former President Sharif Sheikh Ahmed, and is the first parliamentarian to be targeted since a new 275-member assembly was selected in August.
No-one has so far claimed the attack, but al-Shabab has vowed to kill government officials.
On Thursday, a double suicide attack in Mogadishu targeting a restaurant recently opened by Somalis from the diaspora killed 18 people.
Since the overthrow of President Siad Barre in 1991, Somalia has seen clan-based warlords, Islamist militants and its neighbours all battling for control.
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